Crystalline silicon based solar cells having a crystalline silicon substrate are high in photoelectric conversion efficiency, so that the cells have already been used widely and generally as a solar light power generation system. Of the solar cells, the following cell is in particular called a heterojunction solar cell: a crystalline silicon based solar cell wherein an amorphous silicon based thin film having a band gap different from that of monocrystalline silicon is formed on a surface of a crystalline silicon substrate so that a diffusion potential is produced. The heterojunction solar cell, wherein a thin and intrinsic (i-type) amorphous silicon layer is interposed between the conductivity-type amorphous silicon based thin film formed for producing the diffusion potential, and the crystalline silicon, is known as one crystalline silicon based solar cell with the highest conversion efficiency. In this form of solar cell, defects present in the surface of the crystalline silicon substrate are passivated due to the thin i-type amorphous silicon layer. Moreover, the solar cell has the i-type amorphous silicon layer, so that, at the time of forming the conductivity type amorphous silicon based thin film, a carrier-introduction impurity is prevented from diffusing the surface of the crystalline silicon (see Patent Document 1).
Electric current generated by photoelectric conversion is taken to the outside of the cell through its electrodes. The electrodes generally consist of a combination of a transparent conductive layer with a collector electrode. The transparent conductive layer preferably has an optical thickness ([refractive index]×[thickness]) of about ¼ of a wavelength of 300 to 1200 nm, which can be absorbed by monocrystalline silicon. In general, a tin-doped indium oxide (ITO) having a thickness of about 100 nm is widely used as the transparent conductive layer. According to this structure, the transparent conductive layer functions as an anti-reflecting layer by interference of interfacially reflected light on the transparent conductive layer. Thus, the solar cell is made high in light uptake efficiency so that the cell can be improved in photoelectric conversion efficiency.
For the collector electrode, a material such as an Ag paste is used. Such a collector electrode is opaque; thus, in order to enlarge the light-receiving area of the solar cell, at least the collector electrode at the light-incident-side of the cell is patterned into the form of lines by screen printing or some other. This collector electrode is easily peeled from the transparent conductive layer. The peel of the collector electrode is a fatal defect for the operation of the solar cell. For this reason, attempts at improving the adhesive strength between the transparent conductive layer and the collector electrode have been most actively made at present (see, for example, Patent Document 2).